Loans and allowance for credit losses - Allowance for loan losses (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		$ 3,403,000	$ 3,370,000	$ 3,423,000	$ 3,423,000
Provision for (Recovery of) Loan Losses				(400,000)	(300,000)
Charge-offs		(13,000)		(22,000)	(217,000)
Recoveries		33,000		422,000	464,000
Ending Balance		3,423,000		3,423,000	3,370,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 3,272,000
Provision for (Recovery of) Credit Losses	(22,000)		1,000
Charge-offs	(4,000)		(7,000)
Recoveries	10,000		19,000
Ending Balance	3,256,000		3,256,000
Adoption of ASC 326
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			(127,000)
Ending Balance					(127,000)
Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		245,000	271,000	286,000	286,000
Provision for (Recovery of) Loan Losses		(17,000)		(58,000)	(15,000)
Ending Balance		228,000		228,000	271,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	315,000
Provision for (Recovery of) Credit Losses	13,000		20,000
Ending Balance	328,000		328,000
Construction and land development | Adoption of ASC 326
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			37,000
Ending Balance					37,000
Construction and land development | Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		46,000	79,000	57,000	57,000
Provision for (Recovery of) Loan Losses		11,000			22,000
Ending Balance		57,000		57,000	79,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	51,000
Provision for (Recovery of) Credit Losses	10,000		(21,000)
Ending Balance	61,000		61,000
Construction and land development | Residential | Adoption of ASC 326
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			3,000
Ending Balance					3,000
Construction and land development | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		199,000	192,000	229,000	229,000
Provision for (Recovery of) Loan Losses		(28,000)		(58,000)	(37,000)
Ending Balance		171,000		171,000	192,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	264,000
Provision for (Recovery of) Credit Losses	3,000		41,000
Ending Balance	267,000		267,000
Construction and land development | Commercial | Adoption of ASC 326
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			34,000
Ending Balance					34,000
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		2,037,000	2,189,000	1,953,000	1,953,000
Provision for (Recovery of) Loan Losses		150,000		234,000	236,000
Ending Balance		2,187,000		2,187,000	2,189,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,891,000
Provision for (Recovery of) Credit Losses	(96,000)		(118,000)
Ending Balance	1,795,000		1,795,000
Commercial real estate | Adoption of ASC 326
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			(276,000)
Ending Balance					(276,000)
Commercial real estate | Owner occupied
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		892,000	867,000	833,000	833,000
Provision for (Recovery of) Loan Losses		(24,000)		35,000	34,000
Ending Balance		868,000		868,000	867,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	391,000
Provision for (Recovery of) Credit Losses	(12,000)		(13,000)
Ending Balance	379,000		379,000
Commercial real estate | Owner occupied | Adoption of ASC 326
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			(475,000)
Ending Balance					(475,000)
Commercial real estate | Non-owner occupied
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		1,106,000	1,289,000	1,083,000	1,083,000
Provision for (Recovery of) Loan Losses		161,000		184,000	206,000
Ending Balance		1,267,000		1,267,000	1,289,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,460,000
Provision for (Recovery of) Credit Losses	(84,000)		(105,000)
Ending Balance	1,376,000		1,376,000
Commercial real estate | Non-owner occupied | Adoption of ASC 326
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			192,000
Ending Balance					192,000
Commercial real estate | Multifamily
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		37,000	33,000	35,000	35,000
Provision for (Recovery of) Loan Losses		13,000		15,000	(2,000)
Ending Balance		50,000		50,000	33,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	40,000
Ending Balance	40,000		40,000
Commercial real estate | Multifamily | Adoption of ASC 326
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			7,000
Ending Balance					7,000
Commercial real estate | Farmland
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		2,000		2,000	2,000
Provision for (Recovery of) Loan Losses					(2,000)
Ending Balance		2,000		2,000
Consumer real estate secured by 1-4 family residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		210,000	185,000	182,000	182,000
Provision for (Recovery of) Loan Losses		(37,000)		(370,000)	(367,000)
Charge-offs					(27,000)
Recoveries		2,000		363,000	397,000
Ending Balance		175,000		175,000	185,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	322,000
Provision for (Recovery of) Credit Losses	39,000		48,000
Recoveries	4,000		7,000
Ending Balance	365,000		365,000
Consumer real estate secured by 1-4 family residential | Adoption of ASC 326
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			125,000
Ending Balance					125,000
Consumer real estate secured by 1-4 family residential | Home equity lines
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		12,000	11,000	12,000	12,000
Provision for (Recovery of) Loan Losses				(58,000)	(59,000)
Recoveries				58,000	58,000
Ending Balance		12,000		12,000	11,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	33,000
Provision for (Recovery of) Credit Losses	30,000		28,000
Ending Balance	63,000		63,000
Consumer real estate secured by 1-4 family residential | Home equity lines | Adoption of ASC 326
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			24,000
Ending Balance					24,000
Consumer real estate secured by 1-4 family residential | First deed of trust
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		118,000	131,000	123,000	123,000
Provision for (Recovery of) Loan Losses		(5,000)		(11,000)	3,000
Recoveries		1,000		2,000	5,000
Ending Balance		114,000		114,000	131,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	214,000
Provision for (Recovery of) Credit Losses	5,000		11,000
Recoveries			1,000
Ending Balance	219,000		219,000
Consumer real estate secured by 1-4 family residential | First deed of trust | Adoption of ASC 326
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			76,000
Ending Balance					76,000
Consumer real estate secured by 1-4 family residential | Second deed of trust
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		80,000	43,000	47,000	47,000
Provision for (Recovery of) Loan Losses		(32,000)		(301,000)	(311,000)
Charge-offs					(27,000)
Recoveries		1,000		303,000	334,000
Ending Balance		49,000		49,000	43,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	75,000
Provision for (Recovery of) Credit Losses	4,000		9,000
Recoveries	4,000		6,000
Ending Balance	83,000		83,000
Consumer real estate secured by 1-4 family residential | Second deed of trust | Adoption of ASC 326
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			25,000
Ending Balance					25,000
Consumer real estate secured by 1-4 family residential | Consumer and other
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			97,000
Ending Balance					97,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Ending Balance	82,000		82,000
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate)
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		446,000	576,000	486,000	486,000
Provision for (Recovery of) Loan Losses		56,000		(12,000)	180,000
Charge-offs					(157,000)
Recoveries		31,000		59,000	67,000
Ending Balance		533,000		533,000	576,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	549,000
Provision for (Recovery of) Credit Losses	118,000		84,000
Recoveries	6,000		12,000
Ending Balance	673,000		673,000
Commercial and industrial loans | Commercial and industrial loans (except those secured by real estate) | Adoption of ASC 326
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			1,000
Ending Balance					1,000
Commercial and industrial loans | Student loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		63,000	52,000	65,000	65,000
Provision for (Recovery of) Loan Losses		10,000		17,000	18,000
Charge-offs		(13,000)		(22,000)	(31,000)
Ending Balance		60,000		60,000	52,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	112,000
Provision for (Recovery of) Credit Losses	(95,000)		(32,000)
Charge-offs	(4,000)		(7,000)
Ending Balance	13,000		13,000
Commercial and industrial loans | Consumer and other
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		35,000	37,000	29,000	29,000
Provision for (Recovery of) Loan Losses		10,000		16,000	10,000
Charge-offs					(2,000)
Ending Balance		45,000		45,000	37,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	34,000
Provision for (Recovery of) Credit Losses	1,000		3,000
Ending Balance	35,000		35,000
Commercial and industrial loans | Consumer and other | Adoption of ASC 326
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			(5,000)
Ending Balance					(5,000)
Commercial and industrial loans | Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance		367,000	60,000	422,000	422,000
Provision for (Recovery of) Loan Losses		(172,000)		(227,000)	(362,000)
Ending Balance		$ 195,000		$ 195,000	60,000
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	49,000
Provision for (Recovery of) Credit Losses	(2,000)		(4,000)
Ending Balance	$ 47,000		47,000
Commercial and industrial loans | Unallocated | Adoption of ASC 326
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance			$ (9,000)
Ending Balance					$ (9,000)